Combustion supervision system with quantum detector



P. GlUFFRlDA Sept. 7, 1965 GOMBUSTION SUPERVISION SYSTEM WITH QUANTUM DETECTOR Filed Oct. 9, 1961 United States Patent O CMBUSTN SUPERVISION SYSTEM WITH QUANTUM DETECTOR Philip Giuffrida, North Andover, Mass., assignor to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed Oct. 9, 1961, Ser. No. 143,908 1f) Claims. (Cl. Z50-83.6)

This invention relates to combustion control systems and more particularly to an improved comprehensive control system for supervising the existence of flame in a combustion chamber.

An object of this invention is to provide a novel and improved comprehensive combustion control system employing quantum detector apparatus for sensing radiation from the flame source under supervision.

Another object of the invention is to provide a novel and improved control system for supervising the existence of flame in a combustion chamber by sensing ultraviolet radiation from a flame in that chamber.

Still another object of the invention is to provide a novel and improved semi-automatic combustion control system employing a quantum detector for sensing radiation from the supervised fiame source which incorporates coordinated control of ignition and fuel supply to the supervised system in response to signals from the detector.

A further object of the invention is to provide novel and improved circuitry for supervising a combustion system, which circuitry employs transistors compensated so that reliable operation in high ambient temperature environments is assured.

In accordance with principles of the invention there is provided a combustion control systemwhich employs as a flame sensor a quantum detector sensitive to ultraviolet radiation from the flame and optical focusing means for enabling a comparatively small selective area in the combustion chamber to be supervised by the sensitive elements in the quantum detector. The sensing cir- 4cuitry translates any signal resulting from the sensing of iiame into a sine wave signal and couples that sine wave signal to amplifier circuitry which controls a flame indicating relay. The flame relay is coordinated with a control relay which supervises fuel supply and ignition in the supervised system so that any attempt to initiate flame in the combustion chamber will be ineffective if actual flame or a simulated flame ycondition is present in the system. After flame is established the relay circuitry operates, upon detection of any flame failure condition, to terminate fuel supply automatically and to initiate a visual indication or other alarm of the flame `failure condition. In the preferred embodiment of the invention the system employs a novel transistorized amplifier circuit which includes voltage control and thermal compensation that enable the system to be reliably operated in the comparatively high temperature environments normally associated with combustion control systems. The invention thus provides an integrated and reliable ultraviolet radiation llame supervising system which controls the several functional procedures within the supervised system in a coordinated and simplified manner.

Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment of the invention progresses, in conjunction with the drawing, in which:

FIG. l is a diagram of the combustion chamber and associated devices; and

FIG. 2 is a schematic diagram of the combustion control circuitry constructed according to principles of the invention and utilized for the supervision of ame in the combustion chamber shown in FIG. 1.

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The combustion system includes a chamber 10 in which is positioned a main fuel conduit 12 and a pilot burner 14. The flame 16 from the pilot burner extends into the area in front of the main fluid conduit and ignites the fuel flowing from that conduit to produce a main flame 18. Disposed in the wall structure of the chamber so that it can view both the main flame and the end of the pilot flame for detecting the proper length thereof is a detector scanner assembly 2() which includes a quartz lens 22 and a quantum detector tube 24 (IFIG. 2). That detector tube 24 has two electrodes 26, 28 disposed parallel to one another in an envelope 30 that is transparent to ultraviolet radiation and which contains a suitable gas mixture. The lens 22 acts to concentrate ultraviolet radiation on the area of the two electrodes from a larger area that includes both the end of the pilot flame and the main flame so that both flames may be supervised by the single scanner assembly.

An AC signal is applied across the detector tube by a matching transformer 32 which has its secondary 34 connected across the tube and its primary 36 connected to an input transformer section 38 through terminals 40, 42. The transformer winding ratio between wind- ;'ings 34, 36 is such that a 115 input voltage is stepped up to the necessary high voltage for application to the detector tube 24. That high voltage establishes an electrostatic field between. the electrodes and ultraviolet radiation impinging on the negative electrode causes one or more electrons to be released from that electrode, and attracted toward the positive electrode 'at a velocity proportional to the potential difference between those electrodes. Each freed electron in transit collides with the gas molecules which release still more electrons to create an avalanche breakdown in the gas such that the steep wave front pulse is generated and 'applied to the circuitry including the resistors 44 and 46, transformer primary 48 and capacitors 50 and 52. The capacitor 52 and inductance of the transformer primary 48 are proportioned to provide an oscillatory response to an output pulse from the detector tube. Thus, when ultraviolet radiation from the flame impinges on the negative electrode of the tube 24 the resulting current charges capacitors 50 and 52 through the current limiting resistor 44. Capacitor 52 is proportioned so that the Vcharge across it dissipates through the resistor 46 in approximately four milliseconds and the detector tube 24 thus is quenched rapidly after it has fired. The charge across capacitor 50 however discharges through the primary 48 of transformer 54'and builds up an electromagnetic field. When the voltage on the capacitor can no longer sustain the buildup of the field the field collapses producing a charge on the capacitor in the opposite polarity and this ringing operation continues through approximately three cycles for each pulse produced by the radiation tube 24.

The two or three cycle signal is coupled by the secondary 56 of transformer 54 through terminals 58 and 6l) to the inputs of the full wave diode rectifier 62 for application to the amplifier circuitry. The input circuitry of the amplifier includes a load resistor 64, an input capacitor 66, and a resistor 68 connected to the base electrode of NPN transistor 70. The collector electrode of transistor 70 is connected through resistor 72 to the base electrode of PNP transistor 74 and the emitter electrode of transistor 70 is connected to the junction between resistors 78 and 80 in the voltage divider network. The emitter'electrode of transistor 74 is connected to the junction between resistors 76 and 78 and the collector of the transistor 74 is connected to the flame relay coil 82. A feedback resistor 84 is connected between the collector electrode of transistor 74 and the base electrode of transistor 70. Connected between Patented Sept. 7, 1965 the upper terminal of the voltage divider network and the base electrode of transistor 74 is a parallel circuit of thermistor 86 and resistor 88. This thermistor circuit provides a temperature compensated signal to the base electrode of transistor 74 so that the circuitry may operate reliably in environments where the average ambient temperatur-e is 125 F. Power for the amplifier circuitry is supplied from the secondary 90 of transformer 92, which has a thyrite resistor 94, connected across it for voltage surge control 'and a diode 96 which rectifies the voltage applied to the voltage divider network.

When the signal from the detector circuitry charges capacitor 66 sufiiciently positive (to approximately thirteen volts in this embodiment) transistor 70 is turned on and the resulting negative transition is coupled by resistor 72 to the base of transistor 74 turning that transistor on also .and producing a current flow through the collector electrode and the relay coil to energize relay 82. The resulting current fiow from the collector of transistor 74 also causes a three Volt signal to be fed back regeneratively through resistor S4 to the base of transistor 70 to drive the transistors to and maintain them in saturated condition insuring positive operation of the relay coil. In similar manner, when an insufficient signal is present at the base of transistor 70 to maintain its state of conduction the resulting transition at the collector of transistor 74 is fed back through resistor 84 to insure turn off of both transistors `and complete deenergization of relay coil 82.

The combustion control circuit section includes a control relay coil 100 having normally open contacts 102 and 103. In addition normally open contacts 106 and normally closed contacts 108 operated by coil 82 are included in that circuit section which is supplied by transformer 112. Relay 100 also controls normally closed contacts 104 which may be used in an alarm circuit if desired.

A control push button 114 includes a first pair of normally open contacts 116 connected .across the relay contacts 106; a second pair of normally open contacts 118 which control application of power to ignition transformer 120; and a pair of normally closed contacts 122 which control application of power through switch 124 to the main gas solenoid 126 or the main oil solenoid 128 depending on the .setting of switch 124. The pilot burner fuel valve is controlled by solenoid 132 `and switch 130. In addition an alarm 134 is utilized which signals flame failure.

When the system is to be started switch 130 is closed, pe-rmitting the solenoid 132 to be energized as soon as contacts 103 are closed and allowing fuel to flow to the pilot burner 14. The push button 114 is then depressed which bridges contacts 106 land provides a circuit through pilot light 110 for energizing relay coil 100 through the normally closed contacts 108A associated with relay 82. (If there is flame in the combustion chamber or a simulated fiame condition exists in the system, however, relay coil 82 is energized and contacts 108 are open so that no circuit to energize coil 100 can be completed.) The alarm (134) is de-energized when contacts 104 open as a result of the energization of coil 100. Pilot light 110 is energized when contacts 116 are closed, `and contacts 118 complete the circuit to the ignition transformer 120 which is energized when contacts 103 are closed by coil 100. Fuel flowing to pilot burner 14 as controlled by solenoid 132 is ignited by the arc furnished by ignition transformer 120. As soon as ultraviolet radiations from flame in the combustion chamber are sensed by quantum detector 24 the resulting signal operates the amplifier circuitry to energize relay coil 82 closing contacts 106 and opening contacts 108, so that a circuit for holding relay 100 is provided through the contacts 102 and 106. Closing of contacts 106 also shunts contacts 116 and pilot light 110, causing the pilot light to go out and thereby indicating that fiame has been established in the combustion chamber. At

this time push button 114 may be released, opening contacts 118 and de-energizing the ignition transformer 120, .and closing contacts 122 so that the selected main fuel valve, as determined by the position of switch 124, may be energized (through contacts 103) by solenoid 126 or 128. The pilot flame may then be turned off, if desired, by opening switch 130 and de-energizing solenoid 132. In the event of flame failure the signal from detector 24 ceases and relay coil 82 becomes de-energized. Contacts 106 open, dce-energizing the control relay coil 100; contacts 103 open, de-energiing the main fuel valve solenoid; and contacts 104 close energizing the alarm 134.

Thus it will be seen that the invention provides a combustion control system which utilizes detector means sensitive to ultraviolet radiations from the fiame under supervision which incorporates a signal translating circuit that enables the detector to be rapidly restored while providing an output signal of sufficient duration for a .reliable operation of flame relay amplifier circuitry. That amplier circuitry utilizes transistors and includes compensation which enables those transistors to operate reliably in high temperature environments to which the combustion control systems are frequently exposed. in addition, the flame relay is coordinated with a control relay that supervises several control functions associated with the combustion system in a safe, reliable but economical manner. While a preferredembodiment of the invention has been shown and described, various modilications therein will be obvious .to those having ordinary skill in the art and therefore it is not intended that the invention be limited thereto or to details thereof and departures may be made therefrom within the spirit and scope of the invention, as' defined in the claims.

I claim:

1. A combustion control system comprising a quantum detector adapted to be disposed to supervise fiame in a combustion chamber, said quantum d-etector having two spaced electrodes, means to create a high voltage electrostatic field between said electrodes such that an avalanche breakdown between said electrodes will occur when one of said electrodes is exposed to ultraviolet radiation from a flame within said combustion chamber, first current limiting means including a resistor connected in series between said detector and said electrostatic field creating means to limit the flow of current in response to avalanche breakdown, second current limiting means including a parallel resistor capacitor circuit connected in series with said v first current limiting means between said detector and said electrostatic field creating means, signal amplifier cir cuitry, a flame responsive relay connected to said signal amplifier circuitry, and inductive means connected in series with said quantum detector to couple a quantum detector output signal resulting from an ultraviolet radiation produced avalanche breakdown to said signal amplifier circuitry to operate Said liame responsive relay.

2. The system as claimed in claim 1 wherein said inductive means includes an oscillatory circuit connected in circuit with said electrodes arranged to produce a plural cycle output signal in response to each said avalanche breakdown.

3. The system as claimed in claim 1 wherein said signal amplifier circuitry includes a first transistor amplifier stage connected to said inductive means, a second transistor amplifier stage connected between said first stage and said ame responsive relay, and regenerative feedback means connected between the output of saidsecond transistor amplifier stage and the input of said first transistor amplifier stage.

4. The system as claimed in claim 3 wherein one of said transistor stages includes a thermally responsive resistance element connected in circuit between its emitter and base electrodes such that the bias applied to that transistor is adjusted in accordance with the changes in the ambient temperature.

5. The system as claimed in claim 1 wherein said signal amplifier circuitry comprises an amplifier stage including a transistor having emitter, base and collector electrodes and a thermally responsive resistance element connected between said emitter and base electrodes such that the bias applied to said transistor is varied in accordance with the changes in the ambient temperature to which said transistor is exposed.

6. A combustion control system comprising a quantum detector adapted to be disposed to supervise flame in a combustion chamber, said quantum detector having two spaced electrodes, means to create a high voltage electrostatic field between said electrodes such that an avalanche breakdown between said electrodes will occur when one of said electrodes is exposed to ultraviolet radiation from a flame within said combustion chamber, means to concentrate ultraviolet radiation from flame in said combustion chamber on said electrodes, first current limiting means including a resistor connected in series between said detector and said electrostatic field creating means to limit the fiow of current in response to avalanche breakdown, second current limiting means including a parallel resistor capacitor circuit connected in series with said first current limiting means between said detector and said electrostatic field creating means, a flame responsive relay, coupling means including a transformer having a primary winding and a secondary winding, a resistancecapacitance network connected in circuit between said electrodes and said primary winding arranged to produce a plural cycle signal in response to each avalanche breakdown, and means connected to said transformer secondary to apply said plural cycle signal to energize said flame responsive relay.

7. The combustion control system as claimed in claim 6 wherein said plural cycle signal applying means includes a first transistor amplifier stage connected to said transformer secondary, a second transistor amplifier stage connected between said first stage and said flame responsive relay, and regenerative feedback means connected between the output circuit of said second transistor amplifier stage and the input circuit of said first transistor amplifier stage.

8. The combustion control system as claimed in claim 7 wherein one of said transistor stages includes a thermally responsive resistance element connected in circuit between its emitter and base electrodes such that the bias applied to that transistor is adjusted in accordance with the changes in the ambient temperature.

9. Condition sensing apparatus comprising a quantum detector adapted to be disposed to supervise an area of interest, said quantum detector having two spaced electrodes, alternating current supply means to cyclically create a high voltage electrostatic field between said electrodes such that an avalanche breakdown between said electrodes will occur when one of said electrodes is exposed to ultraviolet radiation from within said supervised area, first current limiting means including a resistor connected in series between said detector and said supply means to limit the flow of current in response to avalanche breakdown, second current limiting means including a parallel resistor capacitor circuit connected in series with said first current limiting means between said detector and said supply means, signal amplifier circuitry, condition indicating means coupled to said signal amplifier circuitry, and inductive means connected in series with said alternating current supply means to couple a quantum detector output signal resulting from an ultraviolet radiation produced avalanche breakdown to said signal amplifier circuitry to operate said condition indicating means.

10. Condition sensing apparatus comprising a quantum detector adapted to be disposed to supervise an area of interest, said quantum detector having two spaced electrodes disposed in an ionizable gas, electric current supply means to repetitively create a high voltage electrostatic field between said electrodes such that avalanche breakdown between said electrodes will occur when one of said electrodes is exposed to radiation from within the supervised area, first current limiting means including a resistor connected in series between said detector and said supply means to limit the flow of current in response to avalanche breakdown, second current limiting means including a parallel resistor capacitor circuit connected in series with said first current limiting means between said detector and said supply means, and inductive means connected in series with said supply means to couple a detector output signal resulting from radiation produced avalanche breakdown to signal amplifier circuitry for 0perating a condition indicator.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,821 Whempner Oct. 6, 1942 2,539,208 Schultz et al Jan. 23, 1951 2,594,059 Nagel Apr. 22, 1952 2,721,276 Exner Oct. 18, 1955 2,807,758 Pinckaers Sept. 24, 1957 2,965,828 Wolman Dec. 20, 1960 2,971,134 Cockrell Feb. 7, 1961 3,041,458 Roxberry June 26, 1962 JAMES W. WESTHAVER, Primary Examiner.

FREDERICK L. MATTESON, JR., PERCY L. PAT- RICK, Examiners. 

1. A COMBUSTION CONTROL SYSTEM COMPRISING A QUANTUM DETECTOR ADAPTED TO BE DISPOSED TO SUPERVISE FLAME IN A COMBUSTION CHAMBER, SAID QUANTUM DETECTOR HAVING TWO SPACED ELECTRODES, MEANS TO CREATE A HIGH VOLTAGE ELECTROSTATIC FIELD BETWEEN SAID ELECTRODES SUCH THAT AN AVALANCHE BREAKDOWN BETWEEN SAID ELECTRODES WILL OCCUR WHEN ONE OF SAID ELECTRODES IS EXPOSED TO ULTRAVIOLET RADIATION FROM A FLAME WITHIN SAID COMBUSTION CHAMBER, FIRST CURRENT LIMITING MEANS INCLUDING A RESISTOR CONNECTED IN SERIES BETWEEN SAID DETECTOR AND SAID ELECTROSTATIC FIELD CREATING MEANS TO LIMIT THE FLOW OF CURRENT IN RESPONSE TO AVALANCHE BREAKDOWN, SECOND CURRENT LIMITING MEANS INCLUDING A PARALLEL RESISTOR CAPACITOR CIRCUIT CONNECTED IN SERIES WITH SAID FIRST CURRENT LIMITING MEANS BETWEEN SAID DETECTOR AND SAID 